I recently asked where it was that Chomsky said that in unclear
cases we should let the theory choose the right analysis. The
answer, supplied by Jan Odijk, Barbara Abbott, and Michael Israel
(to all of whom my thanks) turns out to be Syntactic Structures,
p. 14:
...in order to set the aims of grammar significantly it is
sufficient to assume a partial knowledge of sentences and
non-sentences. That is, we may assume for this discussion
that certain sequences of phonemes are definitely sentences,
and that certain others sequences are definitely non-sentences.
In many intermediate cases we shall be prepared to let the
grammar itself decide, when the grammar is set up in the
simplest way so that it includes the clear sentences and
excludes the clear non-sentences. ...A certain number of
clear cases, then will provide us with a criterion of
adequacy for any particular grammar.